The storm left nearly a million customers without electricity and sparked fires across the region.

Rita made landfall at 3:30am (0830 BST) as a category three storm just east of Sabine Pass, on the Texas-Louisiana border, bringing a 6-metre (20ft) storm surge and warnings of up to 64cm (25in) of rain, the National Hurricane Centre said.

Within four hours it had weakened to a category two storm, with top winds of 100 mph, as it moved further inland between Beaumont and Jasper.

There were no immediate reports of fatalities, though rescuers in many areas had to wait for winds to subside before launching searches. About 3 million people had fled an 800km stretch of the Texas-Louisiana coast ahead of the storm, motivated in part by the devastating toll that Hurricane Katrina inflicted barely three weeks ago.

The storm spun off tornadoes as it churned northwest at 12mph, causing transformers to explode in the pre-dawn darkness.

In Jasper County, north of Beaumont, a house with seven people inside floated in floodwaters after it came off its foundation, said the sheriff's communications supervisor, Alice Duckworth.

Ms Duckworth said the 30 emergency workers were stuck in the emergency operations centre because of flooding. "We can't get any fire trucks out," she said.

Rita spared the flood-prone cities of Houston and Galveston a direct hit.

"So far, Houston is weathering the storm," Mayor Bill White said today. His police department received 28 burglary calls overnight and made 16 arrests - less than a typical Friday night, White said.

Rain drenched parts of New Orleans early today, straining the levee system already damaged by Katrina. Up to 8cm (3in) of rain was expected throughout the day, less than had been previously forecast.

"Overall, it looks like New Orleans has lucked out," National Weather Service meteorologist Phil Grigsby said.

Heavy rain fell south of New Orleans in low-lying Jefferson Parish, where a tidal surge of six to seven feet swamped some neighbourhoods. Residents of Lafitte, a town of 1,600 south of New Orleans, were being evacuated by bus.

Fires were reported in and around Houston, including one in a two-story apartment building in south-east Houston that left at least eight units damaged, authorities said. Nobody was hurt, according to district chief Jack Williams.

Several buildings were damaged or destroyed by fire in Galveston, and a blaze broke out before dawn at a shopping complex in Pasadena. There were no immediate reports of injuries.

The US president, George Bush, tracked Rita from an Air Force base in the Rocky Mountain foothills, getting reports on flooding, search and rescue efforts and damage caused by the storm more than 1,600km (1,000m) away.

"It comforts me knowing that our federal government is well-organised and well-prepared to deal with Rita," Bush said in his weekly radio address. "The first order of business now is search and rescue teams - to pull people out of harm's way."

The president also warned coastal residents to wait until authorities say it is safe to return home, because there is still a potential for flooding. His response contrasted with his administration's widely criticised preparations for Hurricane Katrina.

The UN's emergency relief co-ordinator, Jan Egeland, said today that the hurricanes hitting the United States must serve as a "wake-up call" to the world on global warming.

Mr Egeland said that he was convinced hurricanes Katrina and Rita were the result of climate change.

"I think it is a wake-up call for everybody in that you have two of the worst hurricanes ever hitting the US within weeks of each other," he told BBC Radio 4's Today programme.

Scientists are divided over whether the hurricanes are the result of climate change.

Mr Egeland said it was too early to say if the hurricanes had changed perceptions in the Bush administration about climate change. He said no country was adequately prepared for the kind of disasters seen in the US.